Sugar addition in water

[ChemSiddiqui]

Hi,

 

I was taking a lecture when a lad came into the class and asked my chemistry teacher a question. I happened to listen the question and wondered what the answer could be :

 

" Water is a polar molecule. Sugar dissolves in water when its organic compund. Why?"

 

Strange question I know but whats important is to answer it. I thought that the sugar molecule must have either OH or H groups exposed to water when added to water so that it makes a H-bond with it and dissolves but I think I am not right:embarass: ! Any thoughts any one!

[YT2095]

sugar Does have OH bonds, plenty of them, and they are all around the edge for the most part too

 

just have a quick look at Glucose for instance, you`ll see what I mean: http://en.wikipedia.org/wiki/Glucose

[thedarkshade]

Polarized molecule is a molecule that has poles (+ and -). Water for example is a polarized molecule. The polarity of water is due to changes in the value of electronegativity of oxygen and hydrogen. Oxygen has a big electronegaticity value( only F has bigger) so it attracts toward himself the electronic pair (because the bond in water is covalent) and so it is polarized negatively. And so the electrons move a bit away from hydrogen and that causes it to polarize positively.

 

It is this change in electronegativity that makes water molecules possible to create hydrogenic bonds. The positive pole of one molecule is attracted by the negative pole of the other molecule, causing so the hydrogenic bond. And it is hydrogenic bond the reason that gives water some very important features and makes it a key factor for life!

 

Cheers,

Shade

[chemkid]

I was going to post a new thread on this, but since this is here I'll add this:

 

How would one determine whether or not a substance is polar?

 

I understand that it has to do with different electron negativities and the electrons being closer to one atom than another. But how much more electron negative does one element in a compound have to be than the other in order for that compound to be polar? Also how does polarity relate to solubility? Just polar dissolved polar and non-polar non-polar or is there something more?

 

Chemkid

[YT2095]

well in the case of an OH bond it`s always at an angle that leaves the Oxygen slightly (lower case delta) Negative making the H attached to it slightly negative in charge.

 

the H one molecule will have an attraction to the O on another molecule and so on.

 

in H2O this is the case also, enough to form something like a Dipole HH>-O

 

 

hope that helps a little?

[DrDNA]

hey YT,

I think I we are seeing the beginings of chemistry intuition here.

 

 

"The only real valuable thing is intuition." Albert Einstein

 

"Trust yourself. You know more than you think you do." Dr Benjamin Spock

 

"Trust your hunches. They're usually based on facts filed away just below the conscious level." Dr Joyce Brothers

 

"Instinct is the nose of the mind." Madame De Girardin

 

"Knowledge has three degrees-opinion, science, illumination. The means or instrument of the first is sense; of the second, dialectic; of the third, intuition." PLOTINUS.

[Mr Skeptic]

The shape of the molecule will also have and effect on whether it is polar or not. CO2 is nonpolar, CO is polar, H2O is polar. The reason the CO2 is not polar but H2O is is because in the H2O the two H's are rather close together but the two O's in CO2 are 180 degrees apart so cancel.

[psynapse]

I am sorry if this isn't quite correct but I seem to recall that glycerol actually exists in a form called hemiacetal which is to say that a lone pair on the oxygen in the OH farthest from the double bonded Oxygen attacks the double bond of that oxygen forming a tetrahydropurane (cyclohexane with one carbon replaced with an oxygen), now this is stable because all the OH groups are equitorial, not sure if this is the case with sucrose, but perhaps a little insight as to why sugar dissolves in water.

[thedarkshade]

well in the case of an OH bond it`s always at an angle that leaves the Oxygen slightly (lower case delta) Negative making the H attached to it slightly negative in charge.

Yes, I was thinking of that too. In [ce]CO2[/ce] for example the bond is arranged in such angle that the attraction of oxygen by both carbons is the same so the distance of oxygen from both carbons is the same and that's why it is not a polarized molecule. But in [ce]H2O[/ce] the angle of bond is 104.5 and the attraction of hydrogens toward oxygen doesn't really go in a straight line so it causes polarity! [ce]CCl4[/ce] is another example of non-polarized molecule due to the same factor like [ce]CO2[/ce].

[ChemSiddiqui]

WOW! I thought this question was a dull one and that it would produce less answers than any of ones posted earlier by me. Its not the case here tough!. I think every1 is inquisitive for knowledge here. O HAIL CHEMISTRY and GOOD POSTERS!